A conventional aircraft wing has an upper surface, a lower surface, a sharp trailing edge, and a smoothly outwardly curved leading edge. As the angle of attack of the wing increases, the lift provided by the wing also increases until it exceeds a stall angle. Above the stall angle, the airflow separates from the upper surface of the wing and becomes turbulent, and as a result the lift decreases.
A number of control surfaces may be attached to the leading edge of the wing to improve its control or handling characteristics. These include stall strips and leading edge cuffs. A stall strip is a small v-shaped piece of metal attached to the leading edge of the wing. At high angles of attack the stall strip disrupts the boundary layer causing the affected portion of the wing to stall. See for example U.S. Pat. No. 4,702,441. A leading edge cuff is described in U.S. Pat. No. 5,213,287. The cuff extends smoothly from the top surface of the wing to a point forward and below the forwardmost point of the wing, then rearwardly to the bottom surface of the wing. Such leading edge cuffs are believed to increase the stall angle of the wing, as well as making the stall more benign.
Auxiliary aerofoils such as leading edge slats and trailing edge flaps are conventionally provided in order to increase lift during landing and take off, and increase the stall angle of the wing. These auxiliary aerofoils are extended during the landing approach, and before take off, and a gap is generally present between each auxiliary aerofoil and the main wing aerofoil.
Conventionally a leading edge slat is shaped with a cove in its rear face which is a negative image of the outwardly curved leading edge of the main wing aerofoil. A large separated region is present in the slat cove, which gives rise to unsteady flow features that are ultimately responsible for noise generation. These noise sources can be a significant component of the overall airframe noise during take off and landing, and also tend to propagate down, increasing the noise perceived by a person on the ground. A similar problem also exists in relation to the flap and trailing edge of the main wing aerofoil.
One approach to minimising such noise is described in U.S. Pat. No. 6,457,680. A separating surface is provided on the slat and extends in the direction of the main aerofoil along a separation flow line between a vortex flow region and a slat cove flow region. The separating surface may be hinged on a rear face of the flat, or may comprise an inflatable member. A problem with this solution is that the separating surface may compromise the performance of the slat.